In the absence of any event of interest, the insertion error rates are 0.030 and 0.122 for NTU'20 and NTU'21 systems, respectively. When comparing the SELD performances between the 2020 and 2021 setups, the single-source results in 2021 are significantly worse than those in 2020 across all metrics. In addition, the substitution errors across all degrees of polyphony are much higher in the 2021 setup, than in 2020. These results show the detrimental effect of unknown interferences that were introduced in the 2021 dataset, consistent with the findings in [1]}. On the other hand, the two-source results are similar for both datasets even though the NTU'20 and NTU'21 system are completely different, which mean polyphony is also a significant reason for the degradation in the SELD performance.
